The Association Between School Start Time and Sleep Duration, Sustained Attention, and Academic Performance

Figures & data

Figure 1 Pre-post changes in subjective sleepiness and sleep concerns across the school year. Means (and SE) of scores at the Pittsburgh sleep quality index (PSQI) and Epworth sleepiness scale (ESS) at the beginning and end of the academic year.

Figure 2 Academic performance at the beginning and end of the academic year. Means (and SE) of grades at two forms (entrance and final tests) administered in the late and early start classes at the beginning and end of the academic year. ***p≤.001, and “NS” to indicate non-significance.

Table 1 Longitudinal Measures at the Baseline

	Class
	Early Start Class (ESC)	Late Start Class (LSC)	F (1,48)	p	Covariate (Gender) F (1,48)	p
Weekly sleep diary
Light-off hour	11:42pm (0.15)	11:14pm (0.21)	0.03	0.86	0.18	0.67
Total Sleep Time	463.5 (9.5)	441.4 (10.4)	2.58	0.12	0.22	0.64
Sleep Onset Latency	11.23 (1.62)	9.24 (1.77)	19.68	0.66	1.11	0.30
Sleep Efficiency [(Total Sleep Time/Total Bed Time)*100]	92.5 (0.8)	94.9 (0.7)	2.99	0.09	0.95	0.33
Number of Awakenings	0.70 (0.16)	0.71 (0.18)	0.47	0.50	3.94	0.05
Wake-up hour	7:37 (0.13)	7:16 (0.19)	1.99	0.16	0.22	0.64
Psychomotor Vigilance Test (PVT)
Median RT (msec)	291.3 (10.5)	316.1 (10.6)	1.88	0.18	0.21	0.65
Speed	3.48 (0.09)	3.15 (0.09)	4.72	0.03	0.02	0.89
10% slowest RT (msec)	503.9 (35.1)	658.2 (83.0)	4.38	0.04	0.82	0.37
10% fastest RT(msec)	222.3 (5.7)	238.9 (6.2)	3.77	0.05	0.17	0.68
Karolinska Sleepiness Scale (KSS)	3.47 (0.38)	2.38 (0.42)	2.68	0.11	0.21	0.64

Notes: Means (SE) of the weekly sleep diary, Psychomotor Vigilance Task (PVT), and Karolinska Sleepiness Scale (KSS). The table also reports the results of the ANCOVA comparing the two classes (ESC and LSC) with gender considered as a covariate. Bold values denote statistical significance at the p ≤ 0.05 level.

Figure 3 Lights-off hour and bedtime in the two classes across the academic year. Means (and SE) of lights-off hour and bedtime (and, consequently, wake-up hour) in the late and early start classes.

Table 2 Longitudinal Measures

	Class			Month			Class × Month			Covariate (Gender)
	F (1,48)	p	ηp^2	F (5,245)	p	ηp^2	F (5,245)	p	ηp^2	Wilk’s Lambda Rao R (6,43)	p
Weekly sleep diary
Light-off hour	2.39	0.13	0.04	2.43	0.04	0.04	1.71	0.13	0.03	0.90 0.76	0.60
Total Sleep Time	4.52	0.04	0.08	3.55	0.004	0.06	1.90	0.09	0.03	0.99 0.06	0.99
Sleep Onset Latency	0.06	0.81	0.001	1.85	0.10	0.03	1.64	0.15	0.03	0.92 0.65	0.69
Sleep Efficiency (Total Sleep Time/Total Bed Time)	0.81	0.37	0.01	1.66	0.14	0.03	0.45	0.81	0.009	0.90 0.79	0.58
Number of Awakenings	3.17	0.09	0.06	1.13	0.35	0.02	1.09	0.37	0.02	0.68 1.34	0.29
Wake-up hour	9.37	0.003	0.16	6.04	0.00003	0.10	1.78	0.12	0.03	0.90 0.81	0.56
Psychomotor Vigilance Test (PVT)
Median RT	9.51	0.003	0.16	6.41	0.0001	0.11	2.65	0.02	0.05	0.87 1.05	0.41
Speed	3.38	0.07	0.06	9.36	<0.00001	0.16	1.55	0.17	0.03	0.89 0.85	0.54
10% slowest RT	11.06	0.002	0.18	2.98	0.01	0.05	2.82	0.02	0.05	0.81 1.71	0.14
10% fastest RT	1.39	0.24	0.02	4.65	0.0004	0.08	0.92	0.47	0.01	0.93 0.49	0.81
Karolinska Sleepiness Scale (KSS)	0.94	0.34	0.01	1.08	0.37	0.02	0.49	0.78	0.009	0.93 0.53	0.78

Notes: Results of the Class × Month ANCOVAs on longitudinal measures derived from weekly sleep diaries, performance at the Psychomotor Vigilance Task, and self-ratings provided by the Karolinska Sleepiness Scale, with gender considered as a covariate. Bold values denote statistical significance at the p ≤ 0.05 level.

Figure 4 Longitudinal changes in total sleep time and attentional performance across the academic year. Means (and SE) of percentage changes in total sleep time (panel (A) and measures of the Psychomotor Vigilance Task (panel (B) in the late and early start classes. *p≤.05, ***p≤.001.

Figure 5 Lights-off hour, wake-up hour, and total sleep time as a function of school and non-school days. Means (and SE) of (A) lights-off hour, (B) wake-up hour, (C) total sleep time in the late and early start classes plotted as a function of school and non-school days. ***p≤.001, **p≤.01, and “NS” to indicate non-significance.